Plate tectonics and geodynamics - Essay Example

Where does partial melting occur and how do melts reach the magma chamber? Where partial melting occurs Partial melting refers toa process by which a rock does not melt completely. Instead, it is only some part of the parent rock that undergoes the process of melting, producing a hot semi-liquid solution called magma (Best, 2009 p25). The process of partial melting end-up forming rocks that have different composition from their parent rock, since the magma formed during partial melting is less viscous, thus attracts other components which cause it to solidify and form different rocks (Annen & Zellmer, 2008 p49).

Rocks are formed of different mineral components, which have different melting points. Therefore, such components will melt at different temperatures and conditions, a process known as partial melting (Morgan & Chen, 1993 p6285). The process of partial melting takes place in the mantle (Best, 2009 p33). The mantle has four basic components; oxygen, silicon, magnesium and iron which have low melting points. Additionally, the upper mantle, which is below the ridges of the ocean, melts, since it comprises of the lithosphere that is brittle and fractures easily under low temperatures (Griffith, 1998 p67).

Under normal circumstance, the mantle is formed of a solid rock substance called the peridotite (Annen & Zellmer, 2008 53). Partial melting of the peridotite is caused by the heat generated when rocks slide against one another on the base of the lithosphere, causing frictional kinetic energy at the subduction points (Sinton & Detrick, 1992 p198). This generates heat, which causes some elements of the peridotite with a low melting point to melt (Morgan & Chen, 1993 p6289). Consequently, partial melting occurs on the upper mantle, where the peridotite is melt to form a semi-solid substance called the magma (Best, 2009 p30).

How melts reach the magma chamber When the peridotite is melt, the semi-liquid substance formed is less dense than the materials above it. This is because, at such high temperatures, the magma is in a liquid state, which has a low density compared to the solid materials that are on the earth’s crust (Best, 2009 p28). The less dense magma looks for ways to escape upwards and settle above the solid components above it, due to its low viscosity and low density. Therefore, the hotter liquid substance will rise carrying its temperature with it, until it reaches a point where the temperatures are low.

Here, its density is increased through solidification (Griffith, 1998 p70). Oceanic ridges tend to move from one another, creating a channel through which the magma can rise from the mantel of the earth to the earth’s crust (Annen & Zellmer, 2008 p55). Thus, the less viscous magma, which is less dense, follows the divergent boundaries that are created by the oceanic ridges, to reach the magma chamber. Considering that different layers of the mantel are comprised of different substance, partial melting of the peridotite in the upper mantle end-up forming different compounds, when the magma rises and reaches the magma chamber (Sinton & Detrick, 1992 p206).

The process of the magma reaching the surface of the earth begins after the mantel has undergone over 20% of partial melting, which forces the magma formed to squeeze out of the mantel. The magma moves through the crust on to the surface of the earth, in regions called the magma chambers (Best, 2009 p50). ReferencesAnnen, C., & Zellmer, G. F. (2008). Dynamics of crustal magma transfer, storage and differentiation. London: The Geological Society.Best, M. G. (2009). Igneous and Metamorphic Petrology.

Chichester, John Wiley & Sons. Griffith, L. L. (1998). From magma formation to hydrothermal alteration: an integrated study of the Martian crust using thermodynamic modeling of geochemical systems. Washington University, 1998. Morgan, J.P. & Chen, Y.J. (1993).The genesis of oceanic-crust - magma injection, hydrothermal circulation, and crustal flow. Journal of Geophysical Research-Solid Earth 98, 6283-6297.Sinton, J.M. & Detrick, R.S. (1992). Midocean ridge magma chambers. Journal of Geophysical Research-Solid Earth 97, 197-216.